<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            padding: 0;
            margin: 0;
        }

        form {
            width: 640px;
            height: 34px;
            border: 1px solid #333;
            margin: auto;
            padding: 15px;
        }

        form input {
            width: 520px;
            height: 29px;
            border: 1px solid #b8b8b8;
            outline: none;
            padding-left: 10px;
            float: none;
        }

        form input:focus {
            border-color: #3385ff;
        }

        form button {
            width: 90px;
            height: 32px;
            border: none;
            background: #3385ff;
            color: aliceblue;
            float: none;
        }

        form button:hover {
            cursor: pointer;
            background: #095edb;
        }
    </style>
</head>

<body>
    <form action="" method="post">
        <input type="text"><button>百度一下</button>
    </form>
</body>

</html>